The prophets repeatedly denounced their fellow Jews for worshiping at bamot (singular bamah), usually translated as “high places.” Yet other biblical passages seem to suggest that worship at bamot is unobjectionable, as long as God (and not some pagan deity) is being venerated. Although the bamot are generally taken to be hilltop shrines, many archaeologists and Bible scholars think they were actually man-made mounds. What was wrong with them?
The most convincing theory is that after the Temple was built in Jerusalem, it was no longer appropriate to worship elsewhere (1 Kings 3:2) . . . However, when exactly this was understood by historical Israel is harder to determine. Richard D. Nelson of the Perkins School of Theology claims that this was to set the worship of Yahweh apart from the worship of Baal: “The plurality of shrines inevitably reflected the local multiplicity of Canaanite Baal worship, implying a Yahweh of Dan and another Yahweh at Bethel.”
Read more on Bible History Daily: http://www.biblicalarchaeology.org/daily/ancient-cultures/ancient-israel/high-places-altars-and-the-bamah/